The present invention relates to a printed wiring board for use in a various kinds of electronic equipments, and a method of and an apparatus for manufacturing the same.
Double-layered printed wiring boards and multi-layered printed wiring boards enabling a high-density mounting are being spread widely for adoption in electronic equipments along with reduction in size and increase in density of the electronic equipments through the years. In manufacturing process of the double-layered printed wiring boards and the multi-layered printed wiring boards, in the past, drilling has been used to form through holes and blind holes in a substrate. In recent years, however, a new perforation method utilizing a laser beam is emerging as a process capable of making finer holes at higher speed, as disclosed in Japanese Patent Laid-Open Publication, No. H09-107168.
In the prior art perforation method utilizing a laser beam, generally the work has been performed according to a specification for a total amount of radiation energy to be irradiated in a unit area of a substrate. However, there have been cases where dispersion occurs as a result of the work depending on a radiating apparatus, even though the total amount of radiation energy is maintained constant.
Further, another perforation method of the prior art utilizing a laser adopts a process in that a substrate material, as a working object, is evaporated instantaneously in the shortest possible time by irradiating the substrate material with a laser beam having with an enhanced peak energy on the substrate material, in order to reduce an effect of heat to a circumjacent area of the part being processed. However, if the prior art method of laser processing is applied to a substrate having porous structure, a cavity 1a leading to an interior of the substrate can develop in an inner wall of the through hole, as shown in FIG. 15B.
Since a purpose of making the through hole is to form an electric conductive means in the through hole by plating, or by using a conductive paste or the like material for making an electrical contact between an upper and a lower surfaces of the substrate, a development of the cavity 1a leading to an interior of the substrate causes a problem of deteriorating an insulation property of the printed wiring board around the through hole due to an entry of the plated membrane or the conductive paste, as shown in FIG. 16A. A further problem occurs that reliability of the printed wiring board is impaired, if the cavity 1a is present near the surface of the substrate, because a material composing the electric conductive means spreads around the through hole on the surface of the printed wiring board as shown in FIG. 16B.
For the above reasons, the present invention aims at providing a printed wiring board having high density and high reliability, and also a method and an apparatus for manufacturing the printed wiring board of high density and high reliability without decreasing the speediness of the laser processing in the work of perforating the printed wiring board.
The present invention relates to a double-layered and a multi-layered printed wiring board provided with electrical connection means interconnecting a plurality of circuits through a through hole or a blind hole formed in a substrate material in order to connect the circuits constructed with a plurality of metal foils sandwiching an insulation substrate, and a method and an apparatus for manufacturing the same. In the manufacturing process of the printed wiring board of the present invention, the printed wiring board is provided with a preventive means on an inner wall of the through hole or the blind hole for preventing conductive materials constituting the electrical connection means from spreading or permeating into or over the surface of the substrate material.